Electrodeposition of Bismuth Telluride Thermoelectric Films from Chloride-Free Ethylene Glycol Solutions

Electrodeposition of bismuth telluride thermoelectric films is studied and compared in chloride-free and chloride-containing ethylene glycol solutions by means of cyclic voltammograms (CV), electrochemical quartz crystal microbalance (EQCM) and rotating disk electrode (kDE) experiments. It is found that chloride ions strongly affect the tellurium reduction but have almost no effect on the electrodeposition of bismuth. The kinetics of tellurium reduction in chloride-free solutions is three orders of magnitude lower than in chloride-containing solutions, while only a factor of three for bismuth. From chloride-free electrolytes, regular alloy deposition behavior was observed for the bismuth-tellurium system. Equilibrium deposition was obtained under various conditions, mostly at more negative potentials and from tellurium-rich solutions ([Te(IV)]/[Bi(III)]>1). Stoichiometric Bi2Te3 films with a smooth morphology were obtained over the wide potential range. Both p- and n-type films were prepared. The highest Seebeck coefficient was -120 mu V K-1. The chloride-free ethylene glycol electrolytes are highly promising for large scale production of bismuth telluride thermoelectric films as films with well-controlled composition can be deposited at high rates. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.089304jes] All rights reserved.